1. Field of the Invention
The preferred embodiments of the present invention relate to a motor control circuit for controlling revolutions of motors from outside, and more specifically to, a motor control circuit for controlling revolutions of motors from outside using serial communication.
2. Description of the Related Art
The following description sets forth the inventors' knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
Conventionally, in controlling a plurality of motors, it is required to prepare a plurality of drivers corresponding to the number of motors. Therefore, in order to control a plurality of motors, the same number of drivers as the number of motors is required. In recent years, an IC having a plurality of built-in driver functions has become available in the market.
As a structure having a plurality of built-in drivers, for example, Japanese Unexamined Laid-open Patent Publication No. 2007-306637 proposes a multichannel load driving apparatus for driving a plurality of motors.
In the aforementioned IC having a plurality of built-in drivers, however, the IC is merely equipped with a plurality of stand-alone driver ICs. Provided that a single stand-alone driver IC requires ten (10) control terminals except for the power terminal and the ground terminal, in a IC equipped with three (3) stand-alone driver ICs, a total of thirty (30) external terminals are required. Thus, the number of external terminals has not been totally rationalized yet. Motors are required be controlled in real time and that doubling of external control terminals is difficult, and therefore it was difficult to rationalize the external control terminals. For this reason, even if a plurality of drivers are incorporated in a single IC, sufficient advantage due to the rationalization cannot be enjoyed.
In the meantime, when controlling a driver IC from an external microcomputer using signal lines, there is a possibility that the control is performed during the large current changes of the motor. At that time, a large current flows through the motor at the moment of driving the motor, which may cause presence of noise on the ground line of the driver IC. If new setting value is set on the signal line by the microcomputer, the new setting value may be falsely set due to the influence of the noise. False operation due to such false setting may cause damage of the motor.
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. For example, certain features of the preferred embodiments of the invention may be capable of overcoming certain disadvantages and/or providing certain advantages, such as, e.g., disadvantages and/or advantages discussed herein, while retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.